The proper field of view

When designing CCTV camera systems, many people fail to consider what they want to see in the camera’s field of view. John Johnson, in his foundational work for the United States Army, developed what he called DCRI surveillance levels.

Detection: A target is determined to be in the camera’s field of view. Detection applications typically require wide-angle lenses. The lower the lens number, the wider the field of view. For example, a 4mm lens would have a wider field of view than a 12mm lens.

Classification: A target can be distinguished between an animal and an upright human.

Recognition: A human target is determined to be a threat based on the type of clothing and/or the equipment being carried.

Identification: A human target can be identified as a specific individual.

In order to obtain the proper field of view, the correct lens must be installed on the camera.

The best type of lens to use to ensure the proper field of view is obtained is the varifocal lens. There are many different types of varifocal lenses. Some are manual iris, and some are auto-iris lenses. A typical varifocal lens would be 5 to 50mm. For more information on lenses, visit different manufacturer’s Web sites. For example, try Bosch’s Web site at http://products.boschsecurity.us/en/TAMS/products/bxp/CATM40b8fcf5b76c79e176c117fb36cba772.